This project proposes to isolate, purify and characterize a low molecular weight lead-binding protein present in the RBC of lead-exposed workers. An immunoassay for this protein will be developed in order to follow the sequential appearance after initial lead exposure and possible disappearance after chelation treatment and removal from exposure. The proportion between free and bound lead in RBC will be related to the quantity of hemoglobin and low molecular weight binding protein. RBC membrane Na-K-ATPase, determined simultaneously, will be explored as an index of toxicity of free lead on a sensitive enzyme system.